Florida Grade Crossing Repair
THE JOB
Settlement and deflection of precast grade crossing were causing highway pavements to deteriorate. The crossing is owned and maintained by the large business park it serves, is used by CSX, and crosses a major highway maintained by FDOT. Exploratory geotechnical investigations determined that the soil under the crossing had sufficient bearing capacity. However, a void had developed under the crossing, which allowed water to accumulate under the slabs. The slabs deflected under vehicle & rail traffic, which pumped the sandy backfill material out from under the slabs.
The adjacent asphalt had failed, which channeled water into the void below the panels, causing the problem to worsen.
THE CHALLENGE
This Florida grade crossing repair had to quickly and thoroughly address the voids and settlement of the panels. Additionally, the material used for void filling and lifting needed to be resilient under dynamic loading from the train and vehicular traffic, and capable of performing well in saturated environments.
THE SOLUTION
High-density polyurethane grouting to stabilize and lift the affected precast grade crossing panels. Polyurethane grouting is far superior to mudjacking because it allows for rail traffic during the repair and immediate resumption of road traffic. Because the adjacent asphalt had significantly deteriorated, the immediate return to service allowed full-size paving equipment to traverse the crossing immediately after the polyurethane grouting was done.
CJGeo modular grade crossing repair crew filled the voids and corrected settlement in fewer than four hours with CJGrout 48NHL. Milling and paving of the adjacent roadway were done the following day. The roadway and rail opened up immediately afterward.
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Railway Grade Crossing Repair
THE JOB
112 track feet of crossing panels settled, and needed grade crossing repair. This caused the adjacent asphalt pavement to fail. The crossing ran diagonally across the highway. The road was graded so that the crossing was the primary flow path for surface water.
The crossing had already been replaced twice. The last replacement used flowable fill as the base material. The crossing panels experienced approximately 1 inch of deflection with highway traffic. There were also 4-inch voids below the panels.
With highway traffic from heavily-loaded vehicles, the crossing deflected enough to squirt water three to four feet in the air. This water pumping action actively pumped the subbase material from under the crossing.
THE CHALLENGE
The repair had to allow immediate vehicular traffic to facilitate a single-lane closure that was flipped halfway through the repair. The repair also had to allow for immediate resumption of rail traffic. The crossing served a sand mine. so the repair was designed around high service loads for heavy haul rail traffic.
THE SOLUTION
High-density polyurethane grouting using CJGrout 48NHL for this grade crossing repair. CJGrout 48NHL is designed specifically for rail and airfield grouting work.
CJGeo modular grade crossing repair crew filled the voids and corrected settlement in less than a day. Asphalt patching was done concurrently with polyurethane injection. The entire repair took less than one day. The roadway and rail opened up immediately after the repair.
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Industrial Facility Floor Repair
THE JOB
The slab floor inside of a manufacturing facility in Hagerstown, Maryland settled. This caused equipment that was installed on the slab to become misaligned, requiring industrial facility floor repair.
A geotechnical investigation revealed voids below the slab due to the settlement of the underlying soil. The affected area was built over approximately 10 feet of fill during construction. Engineering analysis showed that the soil was likely poorly compacted, but had consolidated with time.
THE CHALLENGE
Due to the sensitive electronic equipment within the work area, the repair had to be very clean and dust-free. Though analysis determined that the underlying soils had most likely completed consolidating, the owner’s geotechnical consultant recommended limiting additional weight placed on the fill material.
The repair area was also more than 100 feet from the nearest exterior access. The floor had started to settle before the equipment was installed. It was very important that the slab not be lifted during the void filling process.
THE SOLUTION
Geotechnical polyurethane grouting to fill the voids below the slab floor. Polyurethane grouting is superior to mudjacking in situations like this because it is considerably cleaner, much faster, and allows for immediate reuse.
The material used in polyurethane grouting is much lower weight than mudjacking grout. This reduces the weight applied to the underlying soil. Lower weight materials reduce the chance of resettlement.
A single CJGeo polyurethane grouting crew completed the industrial facility floor repair in less than a day, using CJGrout 20SDB. Due to the extreme sensitivity of the equipment to lifting, a specially-formulated plural component polyurethane grout was selected for undersealing without lifting.
Precision equipment was used to monitor the floor during undersealing. A movement of 0.02 inches was used to determine the completeness of fill. This was confirmed by extensive extrusion of polyurethane through the adjacent saw cut control joints in the floor. Rotary lasers are the most appropriate for monitoring floor elevations during grouting operations. It’s important to ensure that the base station is well outside the zone of influence of grouting.
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Urban Grade Crossing
THE JOB
32 track feet of grade crossing panels settled. This caused the adjacent asphalt pavement to fail and caused tripping hazards at the adjacent pedestrian sidewalk. The grading in the area was relatively good, however, the adjacent ballast was fouled, which caused water to accumulate under the crossing panels and wash out the sandy subbase material. The crossing had been replaced recently. Due to the urban, primarily passenger automobile traffic, there was a little deflection of the crossing panels from highway traffic. However, there were up to four inches of deflection from rail traffic loading.
The deflection from rail traffic loading caused the top edges of adjacent panels to be in compression with each other. This caused extensive spalling of the surface, which affected two of the panels. While not a functional problem for panel integrity, the spalled areas were within the sidewalk portion of the crossings and therefore posed tripping hazards.
THE CHALLENGE
The repair had to allow immediate vehicular traffic to facilitate a single-lane closure. The repair also had to allow for immediate resumption of rail traffic. The crossing served as a sand mine, so the settlement correction repair was designed around high service loads for heavy haul rail traffic.
Due to the scheduling constraints of the railroad, the repair method had to tolerate the potential for rail traffic during the repair.
THE SOLUTION
High-density polyurethane grouting to stabilize and lift the affected modular grade crossing panels, using CJGrout 48NHL.
Epoxy-augmented patching of the spalled areas to restore a smooth walkway for pedestrians.
CJGeo modular grade crossing repair crew filled the voids and corrected settlement in less than a day. Asphalt patching was done concurrently with polyurethane injection. The entire repair took less than two hours. The roadway and rail opened up immediately after the repair. Traffic control was done to accommodate pedestrians and roadway traffic.
Two trains passed through the crossing over the panels being repaired during the repair. This did not affect the integrity of the repair.
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Alley Settlement Correction
THE JOB
Dewatering associated with a basement excavation caused settlement of an adjacent alley’s pavement. The alley pavement consisted of 4″ concrete base, 2″ course of asphalt, and 3″ thick pavers. The alley served as the sole service and parking entrance to an adjacent residential tower. So, it could not be shut down. Due to the unpredictability of deliveries, the alley settlement correction work also had to allow for intermittent traffic during work.
The pavement had settled up to 3 inches, with nearly 3,000 square feet affected. In addition to being adjacent to two 50+ feet deep basements, one end of the work area was bound by the Navy Yard metro station.
THE CHALLENGE
While the customer was familiar with and inquired about cementitious pressure grouting, CJGeo proposed polyurethane grouting. Polyurethane grouting allows for immediate traffic after repairs, and also for intermittent traffic during repairs. With in-place unit weights of around 4 PCF, polyurethane grouts are significantly lighter than cementitious grouts. This reduces the likelihood of future consolidation of underlying soils.
Polyurethane grouting uses very compact equipment, as well. Instead of large pumps, mixing equipment, and hard to maneuver hoses, polyurethane grouting is all down out of a box truck. Hoses are lightweight, and easy to move out of the way if needed.
THE SOLUTION
A CJGeo polyurethane grouting crew spent two days performing this alley settlement correction project using CJGrout 30NHL. Multiple trash pickups and material deliveries happened during the grouting work. Polyurethane grout effectively cures immediately, ensuring minimal disruption to use of structures during repair.
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Grain Bin Floor Repair
THE JOB
The floor of a 105′ diameter grain bin settled. The floor had a bin sweep installed, that was mounted on the top of the unloading tunnel, which ran down the center of the structure. Where the slab floor butted up to the tunnel walls, the floor had settled 2″ on one half, and 3.5″ on the other half. This caused issues with operating the bin sweep because it was designed for a smooth, level floor.
The owner’s alternative was to remove the entire floor and pour a new floor. This would have been incredibly expensive and taken a very long time. The only access into the bin was two 2′ wide by 4′ tall doors, located 5′ above exterior finish grade, and 2′ above the bin floor elevation.
THE CHALLENGE
Due to the nature of the commodity business, mobilization and completion of the grain bin floor repair had to be fast. Additionally, the repair had to return the floor to its original profile, along with the turned-down ventilation trenches in the floor. The extensive turned-down ventilation troughs made this floor very susceptible to cracking. The floor was 6″ thick but then went to 24″ thick at the ventilation troughs. Slabs with non-uniform thickness require extreme care and attention to avoid differential lifting.
The design loads for the floor are approximately 3500psf. So, the material used for lifting the floor had to be relatively high strength.
THE SOLUTION
CJGeo proposed polyurethane grouting for filling the voids below the floor and lifting them back into place. The minimum bearing capacity of the proposed materials was 5500PSF, ensuring adequate bearing capacity even under full load.
CJGeo mobilized two polyurethane grouting crews to the site. The concrete lifting work was completed over a period of two days. CJGeo placed more than 7,000 pounds of polyurethane grout using three reactors running simultaneously. CJGrout 28FDL is optimal for differential settlement correction, and thus the primary grout. Secondary grouting using CJGrout 20SDB is optimized for undersealing, so chased any nominal voids left by the relatively low mobility CJGrout 28FDL.
Multiple reactors (pumps) helped to ensure thorough lifting of the slab and the ventilation troughs. The crews that completed this job have collectively performed millions of pounds of polyurethane grouting, ensuring the successful completion of this grain bin floor repair job.
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Blower Slab Stabilization
THE JOB
During a routine inspection, extensive voids were discovered under the slab supporting a ventilation blower at a wastewater treatment plant. Staff was concerned that the lack of support under the slab would cause it to settle. As visible in the pictures, this would easily cause extensive damage to this critical equipment.
THE CHALLENGE
The blower slab stabilization repair had to address the voids under the entire area of the slab, including the areas where the slab surface was unaccessible.
Backfill consolidation caused the voids. The roughly 15′ of backfill material under the slab had settled over time. Because the backfill material had been in place for a long time (nearly 20 years), ground improvement wasn’t necessary. The backfill had consolidated as much as it was going to.
THE SOLUTION
CJGeo proposed polyurethane grouting for filling the voids below the blower slab, using CJGrout 20SDB. The minimum bearing capacity of the proposed materials was 3700PSF, ensuring adequate bearing capacity and long-term stability.
CJGrout 20SDB is specifically formulated for high mobility grouting and filling large voids. 20SDB’s tack free time is much longer than its rise time. It can travel very far from each injection point, and doesn’t cause lift. This is helpful in situations like this one, where equipment covers most of the slab, and access is limited. High mobility grouting is excellent for void filling because the material gently fills all voids, without lifting slabs. This is contrast to low mobility grouting, a process designed to displace soils and provide lift.
A CJGeo polyurethane grouting crew filled the voids below the blower base and adjacent sidewalk in less than two hours. The equipment stayed in service during the entire blower slab stabilization repair.
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Warehouse Floor Lifting
THE JOB
25,000 square feet of the industrial floor at a military facility settled up to 4 inches and was affected by sub-slab voids. This warehouse floor lifting project also included 250 track feet of embedded rail, which was set in an independent, thickened slab section. The building had been used for warehousing but was being transitioned to light manufacturing/maintenance.
There were extensive voids below the floor. The voids were located with GPR, and confirmed with cores. Because the floor had cracked extensively as it settled, the designer called for a 4″ un-bonded overlay after stabilization.
THE CHALLENGE
The proposed repair method had to provide adequate bearing capacity for manufacturing and ensure complete void filling and stabilization.
THE SOLUTION
CJGeo provided a value engineering proposal to use geotechnical polyurethane instead of cementitious grout. The VE proposal was based on the following:
- lower unit weight, so less likelihood of causing additional settlement
- adequate strength to ensure uniform load transfer to the underlying soils
- simplified logistics into a secure facility (all material delivered in just two truckloads)
The specified grout had an in-place density exceeding 115 pounds per cubic foot. The proposed polyurethane grout, CJGrout 40NDV, has a constrained density of 5.5PCF, yet a bearing capacity exceeding 12KSF.
CJGeo mobilized three polyurethane grouting crews to the facility, with a combined pumping capacity exceeding 5,000 pounds per hour. CJGeo crews injected the CJGrout 40NDV through nearly 2,000 dime-size holes drilled in the slab to complete this concrete lifting project.
The cutoff criteria for void filling was cross-hole communication or 0.1 inches of lift. The settled areas of floor raised an average of three inches. The embedded track area raised up to four inches.
It took CJGeo fewer than 10 days to complete this warehouse floor lifting job. Because the material cures to 95% within a few minutes, the overlay preparation crew worked a day behind the polyurethane grouting crews.
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Runway Slabjacking
THE JOB
This runway slabjacking project is located in Norfolk, Virginia, at a military base. The hinge slab of a runway at an overpass settled. This caused up to a 1.5″ difference in elevation across the joint between slabs. The slabs had previously been repaired with pressure grouting. The previous runway slab jacking was done using a cement-based grout. The previous slab jacking required drilling 3″ holes on 4′ centers over the entire area. They had to be core drilled due to the 26″ deep slab.
THE CHALLENGE
The proposed repair had to work despite previous repair attempts with cement grout. The repair had to be completed in fewer than 48 hours, with the ability for air traffic at any time during the repair with as few as 10 minutes’ notice. The settled slab was nearly twice as thick as the adjacent slab, which was 14″ thick.
THE SOLUTION
CJGeo proposed polyurethane grouting to raise the settled slabs. Polyurethane grouting allows for immediate resumption of traffic and is much more efficient to install than cement-based grout.
Because the previous repair had left hundreds of 3″ core holes through the slab, polyurethane grouting was idea due to its 5/8″ hole diameter. CJGeo proposed a 6-pound foam (CJGrout 60NHL) for this project, which was originally specified for cement-based grout. 6-pound foam provides adequate bearing capacity and has excellent lifting capacity.
Polyurethane grouting can also be performed in the rain without affecting the material. Due to the extremely short runway shutdown period, the speed of execution despite any bad weather was critical.
CJGeo mobilized three polyurethane grouting rigs to the site for this runway slabjacking project. The joint was saw cut full depth using a 48″ walk-behind saw prior to lifting. Lifting was done using up to four polyurethane reactors running simultaneously. Drilling was completed using a combination of pneumatic rock drills & electric hammer drills.
The runway settlement correction project was completed in less than the allotted time. CJGeo’s subcontracted to TST for this project. The project also includes restriping and asphalt pavement restoration on the runway shoulders.
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9″ Floor Lift
THE JOB
9″ floor lift for 6,000 square feet of slab floor in a flex space building in Boston, Massachusetts. The tenant of a warehouse space vacated at renewal due to challenges that the settlement caused for their operations. The tenant of the adjacent office portion threatened to not renew if the warehouse floor wasn’t lifted.
THE CHALLENGE
The building owner wanted to lift the warehouse floor to improve the function of the space. To avoid further upsetting the office tenant, repairs had to be quiet, dust free, not require moving any of their furnishings, and ensure long term stability.
The office space settlement correction repairs could only happen at night, so relying on material deliveries would be difficult.
THE 9″ FLOOR LIFT SOLUTION
CJGeo proposed plural component polyurethane grouting to the owner for this 9″ floor lift. Plural component polyurethane grouting is exceptionally clean, isn’t dependent on third party grout deliveries, and allows immediately return to service.
A five person CJGeo polyurethane grouting crew corrected all of the settlement in a single shift using CJGrout 28FDL. The vacant warehouse portion of the building was lifted during the day. Once the adjacent office closed for the day, the CJGeo crew completed the office space slab foundation repair overnight.
CJGrout 28FDL injection uses 5/8″ holes drilled through the slab. Because the holes are so small, dustless drilling is very easy. During installation, CJGrout 28FDL expands up to 24 times its liquid volume. Therefore, this entire project was done with material delivered to the site in CJGeo’s equipment. Cement grouting would have required multiple material deliveries, which would have made this 9″ floor lift project take much longer.
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